Thursday, October 28, 2010

Interspecies Sex: Evolution's Hidden Secret?

In a review of the field appearing in the current issue of the journal Nature, the scientist notes that, on average, 10 percent of animal species and 25 percent of plant species are now known to hybridize.

"In the past people have often viewed hybridization as a mistake," Mallet said. "But this is probably not an unnatural phenomenon."

And, he said, "sex with another species may be very occasionally quite a good idea."

Hybridization can increase genetic variability within a population, perhaps offering adaptations particularly suited to new or altered environments.

"It might be worth throwing the dice every now and then to try for something really weird and see if it works out," he said.

Occasionally the act produces sexually fertile hybrids that may have the opportunity to evolve into separate species.

This process in animals involves so-called homoploid speciation, in which the hybrid offspring's DNA is packaged into the same number of chromosomes as the parents' (get a genetics overview).

Homoploid speciation has traditionally been seen as unlikely, because the hybrid could easily breed with its parent species and thus not evolve into its own genetically distinct creature.

But recently identified examples suggest how hybrid species might be able to give themselves room to develop separately.

Last year a team led by Jesus Mavarez of the Smithsonian Tropical Research Institute published details about a hybrid butterfly species from Venezuela and Colombia that appears to use several tactics to isolate itself.

The hybrid butterfly, Heliconius heurippa, inherited yellow wing markings from one parent species and red from the other.

The study team found that both wing colors where needed to attract a mate, so the butterfly tended to breed only with its own kind.

The hybrid insect was also found to live at a slightly higher altitude than either of its two parent species. And the butterfly's caterpillar appears to prefer different plants as food.